In a large, heavy, nonreactive saucepan (aluminum reacts and will cause a pudding to turn dingy gray), combine the milk, ½ cup of the sugar, the vanilla bean, and salt. In a medium bowl, whisk together the yolks, remaining ½ cup sugar, and cornstarch until smooth.
Have the whisk, a ladle, and a large glass or ceramic dish handy. Heat the milk mixture in the saucepan over medium heat until it just comes to a simmering slow boil, whisking it a bit as it gets steamy. When you see the first bubbles boiling up, take the pan off the heat and place it on a potholder next to the egg mixture. (To make life a little easier on yourself, put the egg bowl on the right if you're right-handed, or on the left if you're left-handed. Use your stronger arm to whisk; use your weaker arm to ladle the hot milk.)
During the next steps, stir constantly or the eggs will coagulate and you'll have scrambled eggs. This is quick work. Take a ladleful of hot milk and pour it in a thin stream into the eggs, whisking constantly. Continue stirring, and add one or two more ladlefuls of hot milk to the eggs in the same way. The tempered eggs are now ready to add back into the hot milk.
To do this, whisk the hot milk constantly and slowly pour the tempered eggs in. When fully combined, put this mixture back on the stovetop over medium heat and continue to whisk constantly. The mixture should be ready to come back to a simmer very quickly. When the custard nears the consistency of pudding, take very short pauses in stirring to look for signs of a bubble surfacing (it is more like a single volcanic blurp). Don't look too closely, or you'll risk getting spattered with hot pudding. Just stir, pause briefly, stir, and so on.
When you see the first blurp, remove the pan from the heat immediately and whisk in the cubes of butter. Whisk until fully combined and immediately pour the pudding into a large glass or ceramic dish to cool it down. While the pudding is still very hot, stretch plastic wrap directly on the surface of the pudding. Smooth out any air pockets to make the pudding airtight. This will prevent a skin or condensation from forming on top of the pudding. Refrigerate the pudding until completely cold—at least 4 hours.
Stir the cold pudding and retrieve the vanilla bean. Squeeze out the excess seeds (those little black specks) in the interior of the pod with your thumb and forefinger—pinch and slide your fingers down the length of the bean, freeing the black seeds as you go. Do this with each half of the bean, returning as many seeds as possible to the pudding. Stir the pudding again and pour it into the crust. Smooth the top with a spatula.
Chill the pie, covered with plastic wrap, in the refrigerator for at least 4 hours before serving. It holds for up to 4 days.
This pudding holds very well before it is made up in a pie, so we recommend making 6 cups even if only 3 are needed.
Make the recipe above for half batch of Vanilla Pudding but substitute Crème Fraîche for the milk. Serve with fresh berries.